Fractions Of Poly Research Articles

Thermodynamic parameters of dilute solutions of a polymer in benzene at varying temperatures and concentrations

Dilatometric studies of solutions of four different mole fractions of poly(ethylene glycol) of average molecular mass 400 g mol−1 dissolved in benzene have been performed to estimate molar volumes (V) and volume expansion coefficients (α) at different temperatures. From these, thermodynamic parameters appropriate to these solutions have been evaluated at different temperatures ranging from 299 to 328 K. These parameters have been employed to collect and discuss the information on molecular structure, molecular order, molecular packing, polymer segment extension, and molecular interactions.

Synthesis, characterization and self-assembly of amphiphilic block copolymer poly(4-vinyl benzene chloride)-b-poly(N-vinylpyrrolidone) in aqueous solution

The synthesis, characterization and self-assembly of a novel amphiphilic block copolymer containing a poly(N-vinylpyrrolidone) as a segment of hydrophilic and poly(4-vinyl benzene chloride) (PVBC) arms are reported. The copolymer was characterized by FT-IR spectroscopy 1H NMR. The composition and the molecular weights of the block copolymers were established using gel permeation chromatography and 1H NMR. The water-soluble fraction of poly(N-vinyl-2-pyrrolidone) (PVP)/PVBC block copolymers formed micelles which were investigated at 25 °C in water at 5 mg/ml concentration using a tensiometer. The morphology of micelles in aqueous solution was determined by the AFM, SANS, and SAXS methods.

Preparation and characterization of poly(3-octyl thiophene)/polyvinyl chloride polymer blends

Different weight ratios of poly(3-octyl thiophene) / polyvinyl chloride blends were prepared using the casting method by dissolving poly(3-octyl thiophene) and polyvinyl chloride polymers in chloroform and Tetrahydrofuran, respectively. Fourier transform infrared spectroscopy indicates the existence of carbonyl group in both polyvinyl chloride neat and poly(3-octyl thiophene)–polyvinyl chloride blends. Electrical measurements reveal that the impedance values are increased with the increasing of both weight fraction of poly(3-octyl thiophene) and temperature. Optical results reveal that the increase of poly(3-octyl thiophene) weight fraction in blends enhances the UV-visible absorption of polyvinyl chloride and reduces the optical energy gap of blends. Differential scanning calorimetric measurements and thermal gravimetric analysis show that the glass transition temperature value and thermal stability of blend increases with increasing of poly(3-octyl thiophene) weight ratio. The obtained results, generally, indicate that the increase of poly(3-octyl thiophene) weight fraction enhances the interaction between poly(3-octyl thiophene)–polyvinyl chloride chains and as a result will restrict the chain mobility of polymers.

Effect of thermal history on the evolution of crystal and amorphous fractions of poly[(R)-3-hydroxybutyrate] upon storage at ambient temperature

The manuscript details an investigation on the kinetics of vitrification of the rigid amorphous fraction in poly[(R)-3-hydroxybutyrate] (PHB) in dependence of thermal history. PHB was cooled from the melt at various rates, then the combined evolution of crystal and amorphous fractions was monitored during storage at 25°C. The permanence at room temperature induces progressive growth of PHB crystals and concurrent vitrification of rigid amorphous fraction. During the initial stages of the crystal growth, the amount of rigid amorphous fraction that vitrifies depends on the previous thermal history. After prolonged storage at 25°C, the increase of the crystal fraction corresponds to a reduction of both mobile amorphous and rigid amorphous content. The decreased coupling between the amorphous and crystal segments, reported in the literature for a few other semicrystalline polymers upon annealing at high temperatures, is shown to occur also in PHB, but during crystallization at low temperature. This finding provides one step forward a thorough understanding of the relation between crystal formation and reduced mobility of the coupled amorphous portions.

Morphology and NMR Self-Diffusion in PBA/PEO Miktoarm Star Copolymers

Abstract Morphology and NMR self-diffusion of two miktoarm star copolymers differing in fraction of poly(n-butyl acrylate) and poly(ethylene oxide) (PBA and PEO) arms were under investigation. Structural characteristics of copolymers was obtained on the basis of Small Angle X-Ray Scattering (SAXS) investigations. The phase separated nanoscale morphology of the miktoarm star copolymer with a high fraction of PEO arms was confirmed by Scanning Probe Microscopy (SPM) studies. The modified Avrami approach was used to obtain the information on the non-isothermal crystallization kinetics of the studied systems. It was observed that the crystallization in the system with a higher content of PBA, occurring at higher undercooling, was characterized by a higher crystallization rate. It was also found that increase in PBA arms fraction leads to the reduction in the size of PEO domains. The activation energy of the crystallization process, estimated with Kissinger's method, is lower for miktoarm star copolymer with higher PBA content, which results from facilitation of the transport of PEO chains in the direction of the growing crystal due to the presence of mobile PBA arms. The self-diffusion studies of miktoarm star copolymers melts, carried out with the Pulsed-Gradient STimulated-Echo (PGSTE) Nuclear Magnetic Resonance (NMR) technique, reveals the existence of at least two types of diffusion mechanisms in these systems.

Fractionation of poly(dimethyl siloxane) by interaction chromatography

Poly(dimethyl siloxane) (PDMS) was characterized by interaction chromatography using C4-bonded silica and a mixture of THF/CH3OH as the stationary phase and the mobile phase, respectively. Under the separation condition, a commercial PDMS with broad molecular weight distribution was successfully fractionated according to molecular weight into fractions with a very narrow molecular weight distribution. The IC separation could be applied to more rigorous characterization of PDMS, modified PDMS, and block copolymer-containing PDMS. Open image in new window

Crystalline, mobile amorphous and rigid amorphous fractions in poly(L-lactic acid) by TMDSC

A detailed analysis of the three-phase structure of poly(L-lactic acid) was performed by temperature-modulated differential scanning calorimetry upon quasi-isothermal and non-isothermal crystallizations. The TMDSC analyses revealed that the relative amounts of the three fractions of poly(L-lactic acid) depend on the temperature at which crystallization occurs. It was found that rigid amorphous fraction grows in parallel with crystalline phase during quasi-isothermal crystallization at 90 °C, whereas at T c = 130 °C it starts to appear approximately in correspondence with secondary crystallization. At T c = 135 °C RAF practically does not develop. The results prove that RAF development during crystallization depends on the mobility of the chains. The temperature of complete devitrification at 10 °C min −1 seems to be 130 °C: this temperature could be the limit for the formation and the disappearance of rigid amorphous fraction in the PLLA sample analyzed in the present study.

The effect of molecular weight on the supramolecular interaction between a conjugated polymer and single-walled carbon nanotubes

The synthesis and fractionation of poly[2,7-(9,9-dioctylfluorene)-alt-2,5-(3-dodecylthiophene)] resulted in the isolation of eight different molecular weight (Mw) samples ranging from Mn of 5 to 85 kg mol−1. These individual polymer samples were fully characterized by Gel Permeation Chromatography, Nuclear Magnetic Resonance, as well as absorption and fluorescence spectroscopy. Each sample was separately mixed and ultrasonicated with single-walled carbon nanotubes (SWNTs) in tetrahydrofuran, and the nanotube concentration within the resulting solutions was measured. It was found that the solubility of the polymer–SWNT complexes strongly depends on the Mw of the conjugated polymer, with a maximum concentration reached when Mw ranged between 10 and 35 kg mol−1. Higher and lower Mws resulted in substantially reduced nanotube concentrations.

Impact of Polymer Molecular Weight on the Dynamics of Poly(dimethylsiloxane)−Polysilicate Nanocomposites

Introducing hard spherical polysilicate nanoparticles up to 0.30 volume fraction into narrow molecular weight (M) fractions of poly(dimethylsiloxane) (PDMS) that spanned its unentangled and entangl...

Molecular-hydrodynamic study of poly(N-methyl-N-vinylacetamide) macromolecules

High-velocity sedimentation, translational isothermal diffusion, and viscometry in H2O and DMF are used to investigate the samples and fractions of poly(N-methyl-N-vinylacetamide) synthesized by free-radical polymerization and fractionated in a chloroform-diethyl ether system. Molecular masses M and the Mark-Kuhn-Houwink-Sakurada relations are obtained for the fractions in the molecular mass range M × 10−3 = 3.5−540.0. The negative temperature coefficient of intrinsic viscosity is revealed for both solvents. The length of the Kuhn statistical segment and the hydrodynamic diameter of poly(N-methyl-N-vinylacetamide) macromolecules are estimated; the hydrodynamic volumes occupied by water-soluble poly(N-methyl-N-vinylacetamide), poly(1-vinyl-2-pyrrolidone), poly(vinylformamide), and pullulan molecules are compared.

Heterologous expression of Cupriavidus sp. USMAA2-4 PHA synthase gene in PHB−4 mutant for the production of poly(3-hydroxybutyrate) and its copolymers

Ecological deterioration and human health concerns arising from the usage of non-biodegradable plastics have prompted mankind to search for greener alternatives which are biodegradable, biocompatible and easily produced from renewable sources. Polyhydroxyalkanoates (PHA), among other biopolymers, are emerging as a viable replacement for fossil fuel-based synthetic plastics. A PHA-producing strain, identified as Cupriavidus sp. (designated Cupriavidus sp. USMAA2-4) was isolated from a soil sample from western peninsular Malaysia. Heterologous expression of the PHA synthase gene (phaCUSMAA2-4) in mutant C. necator PHB−4 complemented its PHA-producing ability. More than 60 wt% of P(3HB) was synthesized from various plant oils. The highest P(3HB) production of 2.38 g/l at 68 wt% was attained when crude palm kernel oil was fed as the sole carbon source. The 3HV molar fraction in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] was significantly affected by the type of the precursor used and their respective feeding time. The 3HV molar fraction ranged from 4 to 31 mol% when sodium propionate/valerate was fed at different cultivation times. In addition, with the supplementation of 4HB-monomer precursors, approximately 67 wt% P(3HB-co-4HB) with 4–5 mol% of 4-hydroxybutyrate monomer was synthesized, regardless of the precursor feeding time used. Variation in the molar fraction of the second monomer along with its biodegradability and biocompatibility characteristics promotes the potential of these copolymers as replacements for traditional commodity plastics.

Vitrification and devitrification of the rigid amorphous fraction in poly(ethylene terephthalate)

AbstractVitrification and devitrification of the rigid amorphous fraction (RAF) of poly(ethylene terephthalate) (PET), analyzed during development and disappearance of the three phase structure, are detailed in this contribution. Upon cooling from the melt at a constant rate, the rigid amorphous fraction starts to vitrify when the crystallization process is almost finished, and continues on further cooling. The rigid amorphous fraction is formed in the same temperature range of the secondary crystal growth. Analysis of the low melting endotherm that is observed in isothermally crystallized PET a few degrees above the crystallization temperature reveals a joint contribution of melting and devitrification of the rigid amorphous fraction. The results confirm a link between secondary crystallization and vitrification of the rigid amorphous fraction in semicrystalline polymers. Secondary crystallization takes place in geometrically restricted areas, in which the polymer chains undergo large constraints, so that the mobility of the amorphous chain portions coupled with the crystal phase is reduced. Similarly, the gain in mobility upon partial melting of thinner and/or more defective crystals allows an increase in mobility of the coupled amorphous regions, which results in concurrent mobilization of the rigid amorphous fraction.

Poly I:C Stimulates Sca-1 Expression in Murine Bone Marrow and Increases the Number of Phenotypic Hematopoietic Stem Cells.

Abstract 2504Poster Board II-481Polyinosinic:polycytidlyic acid (poly I:C) is a synthetic double-stranded RNA used to mimic viral infections in order to study immune responses and to activate gene deletion in lox-p systems employing a Cre gene responsive to an Mx-1 promoter. Recent observations made by us and others have suggested hematopoietic stem cells, responding to either poly I:C administration or interferon directly, enter cell cycle. Twenty-two hours following a single 100mg intraperitoneal injection of poly I:C into 10-12 week old male C57Bl/6 mice, the mice were injected with a single pulse of BrdU. Two hours later, bone marrow was harvested from legs and stained for Lineage, Sca-1, ckit, CD48, IL7R, and BrdU. In two independent experiments, each with n = 4, 41 and 33% of Lin- Sca-1+ cKit+ (LSK) IL-7R- CD48- cells from poly I:C-treated mice had incorporated BrdU, compared to 7 and 10% in cells from PBS-treated mice. These data support recently published reports. Total bone marrow cellularity was reduced to 45 and 57% in the two experiments, indicating either a rapid death and/or mobilization of marrow cells. Despite this dramatic loss of hematopoietic cells from the bone marrow of poly I:C treated mice, the number of IL-7R- CD48- LSK cells increased 145 and 308% in the two independent experiments. Importantly, the level of Sca-1 expression increased dramatically in the bone marrow of poly I:C-treated mice. Both the percent of Sca-1+ cells and the expression level of Sca-1 on a per cell basis increased after twenty-four hours of poly I:C, with some cells acquiring levels of Sca-1 that are missing from control bone marrow. These data were duplicated in vitro. When total marrow cells were cultured overnight in media containing either PBS or 25mg/mL poly I:C, percent of Sca-1+ cells increased from 23.6 to 43.7%. Within the Sca-1+ fraction of poly I:C-treated cultures, 16.7% had acquired very high levels of Sca-1, compared to only 1.75% in control cultures. Quantitative RT-PCR was employed to measure a greater than 2-fold increase in the amount of Sca-1 mRNA in poly I:C-treated cultures. Whereas the numbers of LSK cells increased in vivo, CD150+/− CD48- IL-7R- Lin- Sca-1- cKit+ myeloid progenitors almost completely disappeared following poly I:C treatment, dropping to 18.59% of control marrow, a reduction that is disproportionately large compared to the overall loss of hematopoietic cells in the marrow. These cells are normally proliferative, with 77.1 and 70.53% accumulating BrdU during the 2-hour pulse in PBS and poly I:C-treated mice, respectively. Interestingly, when Sca-1 is excluded from the analysis, the percent of Lin- IL7R- CD48- cKit+ cells incorporating BrdU decreases following poly I:C treatment, in keeping with interferon's published role as a cell cycle repressor. One possible interpretation of these data is that the increased proliferation of LSK cells noted by us and others is actually the result of Sca-1 acquisition by normally proliferating Sca-1- myeloid progenitors. This new hypothesis is currently being investigated. Disclosures:No relevant conflicts of interest to declare.

Fractionation of Poly(vinyl acetate) and the Phase Behavior of End-Group Modified Oligo(vinyl acetate)s in CO2

Poly(vinyl acetate) (PVAc) is an inexpensive, high-tonnage bulk commodity polymer which, unlike most vinyl polymers, is moderately biodegradable. PVAc has been shown to exhibit anomalously high solubility in CO2 with respect to other vinyl hydrocarbon polymers. Understanding the phase behavior of PVAc in CO2 and its variation with structure is very important for its potential application as suitable surfactant, ligand, or phase transfer agent in a CO2 solvent process. In this article, PVAc has been fractionated using a supercritical fluid extraction method (SCFE) to provide low molecular weight fractions with narrow polydispersity. The phase behavior of hydroxyl terminated poly(vinyl acetate)s (PVAc-OH) were determined by a high throughput gravimetric extraction (HTGE) screening method and a cloud-point pressure method using a variable volume view cell (VVVC). The solubility of PVAc in CO2 strongly depends on the molecular weight. Oligomer PVAc-OH (Mw < 3000 g·mol−1) is soluble in CO2 at low pressures but decreases in solubility with increasing molecular weight. End-group modification of oligomer PVAc-OH alters the phase behavior of the oligomers.

Fractionation of Poly(vinyl methyl ether): Comparison of Two Large-Scale Fractionation Techniques

The efficiencies of two large-scale fractionation techniques namely continuous polymer fractionation (CPF) and continuous spin fractionation (CSF) are compared. To this end, we used a commercially available sample of poly(vinyl methyl ether). Both methods are suitable to reduce the nonuniformity of the sample below 0.6. The results demonstrate that CSF has a better fractionation performance than the progenitor method, CPF. A further advantage is the three times higher throughput of CSF.

Solid State Photochemistry of Novel Composites Containing Luminescent Metal Centers and Poly(2-methoxyaniline-5-sulfonic acid)

Steady state luminescence and measurements of the luminescent lifetime as well as cyclic voltammetry have been used to elucidate the mechanism and dynamics of interaction between a luminescent ruthenium metal center and two different fractions of poly(2-methoxyaniline-5-sulfonic acid) (PMAS). The two fractions, high molecular weight (HMWT) PMAS and low molecular weight (LMWT) PMAS oligomer, showed significantly distinctive influences on the luminophore. The HMWT PMAS, confirmed to be an emeraldine salt by its characteristic redox chemistry, greatly impacted the diffusion coefficient of the Ru2+/3+ within the composite film, increasing the diffusion coefficient, DCT, by 2 orders of magnitude. The HMWT PMAS also resulted in quenching of the ruthenium-based emission. Significantly, these results indicate that quenching involves both static and dynamic processes, with the static quenching being the dominant process, suggesting that the metal center and polymer backbone were strongly associated. In stark contrast, the LMWT PMAS did not influence the electrochemical properties of the ruthenium metal center; however, it did double the emission observed from the ruthenium metal center. The insensitivity of the luminescence lifetime does suggest that, as with the HMWT PMAS, LWMT PMAS is strongly associated with the ruthenium metal center. The enhanced luminescence may allow for many potential sensor developments based on the luminescent ruthenium metal center, while the HMWT PMAS quenching could be utilized within quenching-based strategies or electrochemical devices.

Continuous production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Effects of C/N ratio and dilution rate on HB/HV ratio

Ralstonia eutropha was cultivated in a continuous stirred fermenter with various C/N ratios (20, 30, and 40), dilution rates, and organic salt substrates (sodium propionate or sodium valerate) to explore the microbial growth and the poly(3HB-co-3HV) accumulation. When sodium propionate was used as the secondary carbon source, the HB/HV molar ratio at various C/N ratios and dilution rates did not change appreciably (approximately 90: 10). The highest poly(3HB-co-3HV) content in biomass (41.8%) and poly(3HB-co-3HV) productivity (0.100 g/(L·h)) occurred under the condition with a C/N ratio of 20 and dilution rate of 0.06 h−1. When sodium valerate was used as the secondary carbon source, the productivity of poly(3HB-co-3HV) increased with increasing dilution rate for the C/N ratio of 30 and 40. The average HB/HV molar ratio ranged from 48: 52 to 78: 32. The feeding of sodium valerate promoted the accumulation of HV better than feeding sodium propionate did. This study shows that a potential strategy of manipulating by both C/N ratio and dilution rate could be used to control the HV unit fraction in poly(3HB-co-3HV) in a continuous cultivation.

Microbial Production of Lactate-Enriched Poly[(R)-lactate-co-(R)-3-hydroxybutyrate] with Novel Thermal Properties

Considerable enrichment of the lactate (LA) fraction in Poly[(R)-LA-co-(R)-3-hydroxybutyrate (3HB)] has been achieved, reaching up to 47 mol % from the previous 6 mol % [S. Taguchi et al. Proc. Natl. Acad. Sci. U.S.A. 2008, 105 (45), 17323-17327], when recombinant Escherichia coli W3110, harboring the LA-polymerizing enzyme gene together with three genes for supplying monomers, lactyl-coenzyme A (CoA), and 3-hydroxybutyryl-CoA, were grown on glucose under anaerobic conditions. The molecular weights of the copolymer were M(n) = 1.5 x 10(4) g/mol and M(w) = 2.0 x 10(4) g/mol, respectively. Notably, alkaline-hydrolyzed product analysis revealed that only the (R)-enantiomer of LA was incorporated in the copolymer. Furthermore, the triad sequence of LA-LA-LA was clearly detected in the polymer chain based on NMR analysis. A remarkably contrasting melting temperature was observed between the copolymer obtained here P[(R)-LA-co-(R)-3HB] (157 degrees C) and the chemically synthesized P[(S)-LA-co-(R)-3HB] (105 degrees C) with similar monomer composition.

Rigid amorphous fraction in poly(ethylene terephthalate) determined by dilatometry

Volumetric thermal analysis of semicrystalline poly(ethylene terephthalate), PET, with different content of crystalline phase was carried out using mercury-in-glass dilatometry. The effect of crystals on the thermal properties of amorphous phase (glass transition temperature, T g, thermal expansion coefficients, α) were determined. At cold-crystallization (106°C, up to 4 h), crystalline content of 2.4–25.3 vol.% was achieved. Increasing content of crystalline phase broadens the glass transition region and increases T g. The change of thermal expansion coefficient during glass transition is lower than that predicted by the two-phase model, which indicates the presence of a third fraction — rigid amorphous fraction (RAF), whose content steadily increases during crystallization. However, its relative portion (specific RAF) is significantly reduced. Further significant decrease in specific RAF appears after annealing at a higher temperature.

X‐ray structural and crystallinity studies of low and high molecular weight poly(3‐hexylthiophene)

AbstractX‐ray diffraction studies were performed in order to understand the crystallinity, the molecular orientation and the nanoscale morphology of a low‐(LMW) and a high molecular weight (HMW) fractions of Poly(3‐hexylthiophene) (P3HT) thin films. The thickness of films was found to be in the range between 10 nm and 200 nm. Further structural information was obtained using X‐ray grazing incidence in‐plane and out‐of‐plane diffraction using synchrotron radiation. The X‐ray analysis reveals that the films are mainly amorphous and contain randomly oriented nanocrystallites with the best match for a monoclinic unit cell. Additionally, polymorphism was found for ∼200 nm thick films of LMW fraction. Interestingly, the film morphology varies as a function of the film thickness. For LMW material the random orientation of nanocrystallites changes to preferential orientation of lamellae along the surface normal when the size of crystallites become of the order of film thickness, i.e. below 20 nm. For the HMW fraction we found an increase of lamellar ordering at about 60 K below the melting point of the material. Temperature‐resolved measurements reveal a thickness dependence of crystallinity. For the LMW fraction the character of the phase transition changes from continuous drop of intensity (for thick films) to sharp drop of intensity for extremely thin films, which is a hint for the importance of the film to substrate interaction. The figure shows the proposed monoclinic unit cell of the P3HT low molecular weight fraction. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)